DESCRIPTION (adapted from the Abstract): Approximately one quarter of patients with the acquired immunodeficiency syndrome (AIDS) develop neurologic symptoms attributable to human immunodeficiency virus, Type 1 (HIV) infection within the brain. Recent studies have shown that all patients with HIV dementia have at autopsy neuropathologic changes consistent with HIV encephalitis. Other studies suggest that HIV- associated neurologic damage may be mediated by immune factors secreted by activated/infected macrophages in the central nervous system (CNS). The Principal Investigator proposes to develop an in vivo system in which viral infection of developing human brain tissue can be studied without many of the in vitro difficulties. In this model dissociated human brain tissue is grown in vitro as a single cell suspension in serum free media; fetal neural cells aggregate and form "brain microspheres" which are then transplanted into the crania of severe combined immunodeficiency (SCID) mice. Pilot studies suggest that brain microspheres injected in the fat pad of SCID mice differentiate and survive for several months in vivo. Study of these grafts shows the presence of functional neural cells and vascular organization suggesting a blood brain barrier. (When brain microspheres are co-cultured in vitro with HIV-infected human macrophages, virus is detected inside the human neural tissue grafts; when the brain microspheres are implanted into a CNS environment, differentiation [i.e., synaptogenesis] is promoted within the graft.) Pilot studies suggest that human fetal brain microspheres can be successfully injected in the crania of SCID mice and surviving grafts can be recovered at different time points post inoculation. In the proposed research, all human grafts will be characterized in vitro prior to implantation. In vivo, grafts will be assessed for neuronal survival and differentiation, development of a blood brain barrier, and CNS macrophage/ microglia activation. Human grafts containing HIV-infected macrophages will be assessed for viral burden, production of macrophage activation factors, and degeneration (i.e., neuronal and glial pathology). Neuropathologic changes found in HIV-infected grafts will be then compared to the findings in autopsy studies of patients with HIV encephalitis. In this human fetal brain/SCID mouse model, both qualitative and quantitative measurements of viral and immune factors can be performed, neuronal differentiation can be studied, and the perturbations caused by addition of HIV-infected macrophages can then be temporally monitored to help elucidate the pathogenesis of neurologic damage.